In vehicles equipped with automatic transmissions, the park function is typically accomplished by locking the drive wheels of the vehicle through the transmission to ground. The wheels are generally held by engaging a parking pawl into a dedicated parking gear that is connected continuously with the wheels through the transmission output shaft. One such device is shown in U.S. Pat. No. 2,875,856 issued Mar. 3, 1959, to Mrlik et al.
Since the parking pawl prevents the wheels from turning by grounding them to the transmission case, the strength requirements of the pawl must generally be taken by a single tooth design mated to a gear having complementary teeth formed thereon. This results in designing the gear with a circular tooth thickness large enough to withstand the parking forces. The pawl is also designed with a pressure angle of approximately 16 degrees to provide for control of the push out force on the pawl during parking. This push out force must be maintained with any range, such that excessive pull out forces are not required when the transmission is parked on a steep grade.
There have been some consideration given to multi-tooth park mechanisms, however, these mechanisms do not generally provide the resistance to sheer loads that are desired.